1. Field of the Invention
The present invention relates to a network, a network terminal device, an IP address management method using the same, and a program therefor, and more particularly relates to a system that enables IP telephones and other terminals to connect to a LAN (Local Area Network) in a remote environment using DHCP (Dynamic Host Configuration Protocol).
2. Description of the Related Art
In a conventional network system that includes a network terminal such as an IP telephone, operation using DHCP is not implemented in networks in which backup system control devices are used.
In this case, DHCP is an arrangement for dynamically providing host-setting information in the TCP/IP (Transmission Control Protocol/Internet Protocol) network, and can, on the basis of the BOOTP (Bootstrap Protocol), dynamically provide time-limited IP addresses from the DHCP server to a client (Refer to “Dynamic Host Configuration Protocol 3 The Client-Server Protocol” [RFC (Request For Comments: 2131, March 1997, Page 13 to 22)], for example).
An example of operation in a remote location in which DHCP is used is a system that can acquire an address by DHCP even with a user terminal device installed in a remote location (Japanese Patent Application Kokai Publication No. 2001-189761, for example). In this first prior art, a user terminal device is connected to a remote access server apparatus via a dialup server unit. The dialup server unit responds to an incoming transmission from the user terminal device and then sends to an authentication server the user identifier and password received from the user terminal device. The authentication server authenticates the identifier and password, after which the DHCP message transmission unit is instructed to acquire an address by way of a network host address interrupt request from the user terminal device, and the DHCP message transmission unit acquires a network host address and notifies the user terminal via the dialup server unit.
An example of operation in which a backup system control device is used is a system which can operate during malfunctions by providing a backup switching device (Japanese Patent Application Kokai Publication No. 10-15046, for example). In the second prior art, a device having a plurality of frame relay switchers is provided for transferring the stored position information of the communication remote terminal to a backup frame relay switcher and making a backup connection when a circuit malfunctions in a frame relay network that communicates by a remote fixed connection. The back frame relay switcher makes a backup connection to a terminal by way of a backup circuit on the basis of the stored position information.
However, when an attempt is made to connect an IP telephone or another terminal to a LAN in a remote environment by using DHCP, the time limit of the IP address that the telephone terminal previously acquired from the DHCP server must be updated before the time limit elapses. Nevertheless, in the conventional network described above, when a malfunction occurs in the transmission line between the DHCP server and a telephone terminal equipped with a DHCP client function, the usable IP address information is no longer available because the telephone terminal can no longer carry out the update routine for updating the IP address time limit. As a result, there is a problem in that a connection can no longer be made to the system control device installed as a backup. For this reason, operation using DHCP cannot be carried out in a network in which a backup system control device is used in a network system having a network terminal such as an IP telephone.